Modern mobile telecommunications standards continue to demand increasingly greater rates of data exchange (data rates). One way to increase the data rate of a wireless communications device is through the use of carrier aggregation. Carrier aggregation allows a single wireless communications device to aggregate bandwidth across one or more operating bands in the wireless spectrum. The increased bandwidth achieved as a result of carrier aggregation allows a wireless communications device to obtain higher data rates than have previously been available.
FIG. 1 shows a table describing a number of wireless communication operating bands in the wireless spectrum. One or more of the operating bands may be used, for example, in a Code Division Multiple Access (CDMA), Global System for Mobile Communications (GSM), Long Term Evolution (LTE), or LTE-advanced equipped wireless communications device. The first column indicates the operating band number for each one of the operating bands. The second and third columns indicate the uplink and downlink frequency bands for each one of the operating bands, respectively. Finally, the fourth column indicates the duplex mode of each one of the operating bands. In non-carrier aggregation configurations, a wireless communications device will generally communicate using a single portion of the uplink or downlink frequency bands within a single operating band. In carrier aggregation applications, however, a wireless communications device may aggregate bandwidth across a single operating band or multiple operating bands in order to increase the data rate of the device.
FIG. 2A shows a diagram representing a conventional, non-carrier aggregation configuration for a wireless communications device. In this conventional configuration, a wireless communications device communicates using a single portion of a wireless spectrum 10 within a single operating band 12. Under the conventional approach, the data rate of the wireless communications device is constrained by the limited available bandwidth.
FIGS. 2B-2D show diagrams representing a variety of carrier aggregation configurations for a wireless communications device. FIG. 2B shows an example of contiguous intra-band carrier aggregation, in which the aggregated portions of the wireless spectrum 14A and 14B are located directly adjacent to one another and are in the same operating band 16. FIG. 2C shows an example of non-contiguous intra-band carrier aggregation, in which the aggregated portions of the wireless spectrum 18A and 18B are located within the same operating band 20, but are not directly adjacent to one another. Finally, FIG. 2D shows an example of inter-band carrier aggregation, in which the aggregated portions of the wireless spectrum 22A and 22B are located in different operating bands 24 and 26. A modern wireless communications device should be capable of supporting each one of the previously described carrier aggregation configurations.
The various carrier aggregation configurations discussed above can be performed between two or more frequency division duplexing (FDD) bands, two or more time division duplexing (TDD) bands, or a combination thereof. Generally, a wireless communications device will aggregate bandwidth when receiving data (i.e., during downlink), but will use a single operating band when transmitting data (i.e., during uplink). However, carrier aggregation may also be used during data transfer to increase uplink throughput.
FIG. 3 shows conventional front end circuitry 30 for a wireless communications systems capable of operating in one or more carrier aggregation configurations. The conventional front end circuitry 30 includes an antenna 32, a diplexer 34, a first duplexer 36A, and a second duplexer 36B. The diplexer 34 is coupled between the antenna 32, a first input/output node 38A, and a second input output node 38B. The first duplexer 36A is coupled between the first input/output node 38A, a first transceiver node 40A, and a second transceiver node 40B. The second duplexer 36B is coupled between the second input/output node 38B, a third transceiver node 40C, and a fourth transceiver node 40D.
When receiving, RF receive signals from the antenna 32 are provided to the diplexer 34, where they are separated into high-band RF receive signals and low-band RF receive signals. The high-band RF receive signals are delivered to the first input/output node 38A, while the low-band RF receive signals are delivered to the second input/output node 38B. The first duplexer 36A then isolates RF receive signals within one or more high-band operating bands from the high-band RF receive signals, delivering the isolated RF receive signals to the second transceiver node 40B. Similarly, the second duplexer 36B isolates RF receive signals within one or more low-band operating bands from the low-band RF receive signals, delivering the isolated RF receive signals to the fourth transceiver node 40D.
When transmitting, an RF transmit signal is provided to one of the first transceiver node 40A and the third transceiver node 40C. Specifically, one of a high-band RF transmit signal and a low-band RF transmit signal is provided to the first transceiver node 40A and the second transceiver node 40B, respectively. Filtering is performed on the RF transmit signal as it passes through either the first duplexer 36A or the second duplexer 36B, depending on the origin of the RF transmit signal. The RF transmit signal is then delivered to the antenna 32 via the diplexer 34.
Due to the configuration of the diplexer 34, the first duplexer 36A, and the second duplexer 36B, the conventional RF front end circuitry 30 is capable of operating in carrier aggregation configurations between a high-band operating band and a low-band operating band, however, the performance of the circuitry may be limited when transmitting RF signals. As will be appreciated by those skilled in the art, the diplexer 34, while necessary to ensure that the conventional RF front end circuitry 30 can isolate and thus simultaneously receive signals within the high-band operating band and the low-band operating band, adds significant insertion loss into the transmit path of the conventional RF front end circuitry 30. This in turn degrades the efficiency of the circuitry when transmitting RF signals and thus reduces the battery life of a wireless communications device in which the conventional RF front end circuitry 30 is incorporated.
FIG. 4 illustrates a TDD frame 42 for an LTE network according to one embodiment of the present disclosure. As shown in FIG. 4, the TDD frame 42 is divided into a number of timeslots 44. Each timeslot is designated for a certain function, such as downlink (DL), in which RF signals are received by a wireless communications device, uplink (UL), in which RF signals are transmitted by a wireless communications device, special (S), which is used to transition between downlink and uplink modes, or some combination of the above. In a TDD architecture, a wireless communications device will generally allocate the timeslots 44 according to instructions from a base station or internal logic within the device itself.
As discussed above, the conventional RF front end circuitry 30 may be capable of aggregating one or more TDD bands in order to simultaneously receive signals at two different frequencies during a downlink timeslot 44. However, the RF filtering circuitry required to support such a carrier aggregation configuration generates significant insertion loss in a transmit path of the conventional RF front end circuitry 30, thereby leading to reduced performance during an uplink timeslot 44.
In light of the above, there is a need for improved RF front end circuitry for carrier aggregation configurations. Specifically, there is a need for RF front end circuitry with improved performance when aggregating bandwidth between two or more TDD operating bands.